The present invention relates to a so-called heating trowel which process the working material by heat while observing its status, such as soldering iron, plastic welder, iron, hair iron and the like, and specifically it relates to a heating trowel that could be used within a few seconds from providing power.
Conventional heating trowels such as soldering irons are of simple structure which provides fixed electricity to fixed heating wire, and using it at a temperature of thermal equilibrium condition. In addition, trowels with large heat capacity are preferred, therefore the time needed for heating to appropriate temperature took from 3 to 5 minutes. There are trowels which require only about 30 seconds for heating, but it is small in heat capacity and is easy to overheat, therefore it needed very precise and expensive control mechanism.
Also there are soldering irons which use assistant heater working while a switch is pressed along with an ordinary heater, being conveniently used when the working material has large heat quantity. However, the user might lose track of time after 4 or 5 seconds of pressing the button, therefore in order to prevent overheating from overpressing, the heating ability must be weakened. Accordingly, it took 15 to 20 seconds to heat even when the assistant heater is used at the beginning.
The heater used in such heating trowels is made by winding a Nichrome wire to micaceous thin plate, or holding the wire between the thin plates. Therefore, the generated heat is only transferred slowly to the trowel tip, being obstructed by mica which is a superb heat insulator. Also, large temperature difference is needed, so that the heating wire is heated to near its melting point, making its life short.
There are trowels enabling process in a matter of seconds, such as a large module for soft soldering numerous terminals of IC or LSI with fixed shape at once by providing electric current of about 500 A. However, it is large in size, and could not conveniently be used in cases where shape and heat capacity of the working material change.
A trowel using ceramic heater made by baking metal oxides to ceramics such as aluminum oxide is utilized. However, because only small amount of electricity could be provided, the heat value per area is not so big. Also, the thermal conductivity of the aluminum oxide is in the same level as the stainless steel, so that it took time for the heat to reach the trowel tip/heat storage.
An aluminum nitride having high thermal conductivity has high sintering temperature, therefore it is technically difficult for the conductive material suitable for heating wire to be sintered firmly. Also, there is a difficulty in durability from thermal expansion and thermal shrinkage.
The conventional heating trowels therefore did not heat rapidly, so that danger arising from leaving the switch on such as forgetting about it while heating, forgetting to turn off the switch when interrupting work and almost catching fire, or being burnt from heated trowel tip and the like occurs many times. There is no inconvenience in working continuously for a long period of time. However, it is not suitable for using quickly on small amount of work, or for intermittent work. Therefore, there is a need for heating trowel that could be used immediately, and that could be controlled simply and inexpensively.
A heating trowel is comprised of a heating wire made of metal plate such as iron chrome alloy and which is thinned to the limit of maintaining its shape, an electrical insulator which is a thin plate of aluminum nitride and the like having more than 10 times the heat conductivity of the heating wire, and a trowel tip/heat storage made from copper and the like having more than twice the heat conductivity of the aluminum nitride and the like and also having high heat capacity, and formed by sufficiently adhering these components closely by pressing and the like using a heat insulating supporter.
The control method comprises providing a fixed large amount of electricity for a fixed short period of time to a heating wire by operating a power switch once and rising the temperature of a trowel tip/heat storage rapidly within the temperature range suitable for processing the working material, or in a temperature range of a half or one third of the suitable temperature range, and obtaining a desired temperature by pressing the switch for a countable number of times.